1. Field of the Invention
The invention is generally directed to a method using tribopolymerization for reduction of tool wear and friction between a ceramic cutting tool and a workpiece in machining/cutting applications while improving the surface finish imparted to the reshaped workpiece.
2. Description of the Prior Art
A typical metal machining operation involves creating a new shape in a workpiece by removing surface material from the workpiece in a controlled manner. The creation of such new shapes by removal of stock material from the workpiece generates high friction and high temperature, which conditions can cause and aggravate tool wear. The sources of heat mainly emanate from the shear zone and tool-chip interface zone. The highest temperature zone typically is at the tool-chip interface zone (friction zone) where crater wear of the cutting tool occurs.
Therefore, metal cutting lubricants have been used in the past in efforts to mitigate the effects of frictional forces and heat stresses to which a machining tool is subjected. Such cutting fluids have been used for various objectives, including: cooling and controlling the tool and workpiece temperature to minimize distortions and/or tool wear; lubricating and reducing friction between the tool and workpiece (and removed surface chip) to reduce tool wear; and facilitating swarf removal to improve surface finish and/or reduce tool wear. The type of workpiece, e.g., its hardness, the nature of the machining operation to be performed, and severity of the operation, will influence the choice of cutting fluid employed.
Conventional cutting fluids for machining operations on nonferrous (softer) workpieces include, for example, general-purpose or clear-type, fatty soluble oils. For machining low-carbon and medium-carbon steels, or in machining operations such as grinding, turning, milling and drilling operations on high hardness workpieces (e.g., high-carbon and alloy steels and stainless and heat-resistant alloys), extreme-pressure soluble oils (e.g., containing sulfurized or chlorinated extreme-pressure additives) or synthetic chemical cutting fluids (e.g., containing rust inhibitors) have been used.
So-called neat cutting fluids have been required in high hardness workpieces for gear shaping, hobbing, broaching, tapping, and some drilling operations. Such neat cutting fluids include, for example, a very low viscosity, inactive oil containing fatty and chlorinated additives; an inactive oil containing sulfurized fatty extreme-pressure additive; a multipurpose, chlorinated extreme-pressure oil with anti-stick-slip additives; an active oil containing free sulfur and sulfurized fat; an inactive, extreme-pressure oil containing chlorinated and fatty additives; a low-viscosity, active oil containing free sulfur and sulfurized fatty additives; and a special-purpose, highly-chlorinated, active extreme-pressure oil.
While the above-mentioned types of cutting fluids may be effective for conventional machining operations, the machining industry constantly seeks to improve productivity and reduce costs by increasing cutting speed in machining, among other things. These more vigorous machining operations desired place new and greater demands on the cutting fluid. For example, high speed machining (HSM) involves increasing peripheral cutting speeds significantly higher than those currently used in most machine shops. For instance, the maximum peripheral cutting speeds associated with current high speed machining operations range from less than 2.54 m/s (500 surface feet per minute) for titanium alloys, to about 5.08 m/s (1000 sfpm) for nickel-based alloys.
Therefore, under the conventional wisdom, one might surmise that these more severe machining operations associated with high speed machining would tend to demand more active cutting fluids. This might suggest that cutting fluids with additives, particularly extreme pressure ones, would be required for such severe operating conditions. However, as it turns out, prior high speed machining with ceramic tools has been carried out under dry conditions because the use of conventional liquid lubricants, such as mineral-oil based and water-based lubricants, increase thermal-mechanical shock and/or corrosion. Such thermal-mechanical shock causes fracture and chipping of the ceramic tool. However, the ability to dry cut a metal workpiece with no lubricating fluid is very limited, an example being the machining of cast iron or super-alloys such as Inconel 718 with cubic boron nitride (CBN) compacts.
U.S. Pat. No. 5,407,601 (Furey et al.) discloses certain fluid compositions comprised of a monomer constituent dissolved in a carrier fluid, where the monomer constituent is capable of forming a polymer film directly on rubbing ceramic surfaces but is not polymerized in solution. The fluid composition is effective for reducing wear in the rubbing ceramic surfaces. U.S. Pat. No. 5,407,601 patent relates to using the fluid composition as a lubricant for rubbing surfaces, and it seeks to reduce wear of material from either of the rubbed surfaces.
The present inventors have found a mode of reducing tool wear and friction in machining operations which significantly increases ceramic tool life and improves surface finish of the workpiece with minimal environmental impact and problems, and without causing thermal-mechanical shock in the friction area, or corrosion of a metal workpiece.